This invention relates to a device for conveying photographing films (hereinafter referred to as "films"), and more particularly to a film conveying device in which a fog problem (hereinafter referred to a "a static problem") caused by the discharge of static electricity when a film held between a pair of flexible belts (hereinafter referred to as "belts") is conveyed, is prevented.
In general, a variety of devices which convey a film by holding it between belts are employed for photographing apparatuses or processing apparatuses which handle films.
For instance, a film conveying device as shown in FIG. 1 is employed for a medical X ray type automatic photographing apparatus. In this conventional device, an X ray film 1 is held between fluorescent latensification sheets 8 and 9 bonded to a pair of belts 3 and 4 and is conveyed to a predetermined position by means of conveying rollers 5, 6 and 7. After completion of an X ray photographing operation, the film 1 is returned to the position where it was inserted thereinto, and then the film 1 is removed from the film conveying device. In the conventional film conveying device of the medical X ray type photographing apparatus, when the belts 3 and 4 are wound or rewound, the belts 3 and 4 are electrically charged by friction and the separation of the belts. The electric charges are discharged between the belts and the X ray film 1, or between the belts and the latensification sheets 8 and 9. The discharge usually occurs when the X ray film 1 held between the belts is conveyed, or when it is taken out of the latensification sheets 8 and 9; as a result of which the static problem is often caused.
Heretofore, the following methods have been employed to prevent the static trouble. In one conventional method, a metal brush or metal braid is brought into contact with the conveying belts 3 and 4 to remove the static electricity charge therein. In another method, positive and negative ions are generated by a corona discharge type electricity remover, thereby to eliminate the charges. In a third known method, electrically conductive belts are made of flexible plastic or rubber sheets which contain a charge preventing agent such as carbon black, or a surface active agent to prevent the charging of the belts.
However, the method using the metal brush or metal braid is insufficient in charge removing effect. The method using the corona discharge type electricity remover is disadvantageous in that the discharge often gives fogs to the films. Furthermore, the method using the electrically conductive belts containing the charge preventing agent is not effective unless a large amount of charge preventing agent is used. If a large amount of charge preventing agent is used, the strength and durability of the belts are reduced, and accordingly the belts may be worn or broken when used repeatedly. These drawbacks become more significant because recently the operating speed of the photographing apparatus has been made considerably higher.